The present invention relates to a miniaturized device for the detection of characteristics of a fluid. The device according to the invention finds advantageous, even though not exclusive, application in the measurement of performance of a lubricating oil, directly on a system or an apparatus that uses the oil itself, such as for example an internal-combustion engine.
By now widely shared is the conviction that only a simultaneous measurement of many parameters enables a satisfactory characterization of the conditions of wear and contamination of a lubricating oil. Amongst said parameters of particular importance is the lubricating capacity of the oil.
In the laboratory, the oils can be conveniently tested using tools dedicated thereto, referred to as tribometers, which are able to measure quantitatively the characteristics of lubricating efficiency of the oils. On systems and apparatuses that use lubricating oils, such as an internal-combustion engine, the characteristics of the oils are instead detected via appropriate sensor devices. Said devices are generally designed to deduce conditions of wear and contamination of the lubricating oils on the basis of the measurement of parameters such as viscosity, temperature, conductivity, opacity, dielectric constant, just to mention the ones most widely taken into consideration.
The patent document No. U.S. Pat. No. 4,966,032 describes a instrument for monitoring a lubricating oil, equipped with supporting means that comprise a basic body, which has a surface of contact that can be submerged in the lubricating oil. Associated to the basic body is a lamina-like element, which can be set in vibration and has a portion of contact that rests on the aforesaid surface of contact. Associated to the lamina-like element are actuator means, designed to cause vibration of the lamina-like element, and sensor means for detecting a vibration of the lamina itself caused by the friction between said portion and the surface of contact to produce an output signal of the sensor. The sensor means and the actuator means are made of piezoelectric material.
The patent document No. EP-A-0 675 355 describes a sensor element for detecting solid particles in a fluid, such as a lubricating oil, comprising a cantilever element of dimensions such as to enable its vibration following upon a collision with a solid particle, and means for converting a vibration of the cantilever element into an electrical signal. The aforesaid means are formed by a film made of piezoelectric material. A possible embodiment envisages the use of a plurality of cantilever elements, a first one of which is used as sensor for detecting the solid particles and a second one of which is used as sensor to obtain a reference parameter necessary for the purposes of the measurement. A third cantilever element can possibly be set in vibration via the respective piezoelectric means (by inverse piezoelectric effect), so as to exploit said vibration for the purposes of detecting the degree of viscosity of the fluid.
Notwithstanding the vast literature on the subject, there has not yet been proposed a miniaturized sensor for monitoring the conditions of lubricating efficiency of a generic fluid, such as an oil.